1. Field of the Invention
This invention relates to compositions prepared from solid acyl alkylsulfonyl peroxides and polar or polarizable solvents or solvent mixtures. These novel compositions are used as free-radical initiators for vinyl monomer polymerization processes.
2. Description of Prior Art
Acyl sulfonyl peroxides such as acetyl cyclohexylsulfonyl peroxide (ACSP) have found increasing use in polymerization and copolymerization of vinyl monomers such as vinyl chloride and vinyl acetate. These initiators are especially useful for increasing the output of polyvinylchloride (PVC) reactors when used in combination with dialkyl peroxydicarbonates. Normally, a vinyl chloride polymerization which employs only a dialkyl peroxydicarbonate suffers through an initial induction period in which little PVC is produced. By using acyl sulfonyl peroxides such as ACSP in combination with dialkyl peroxydicarbonates a rapid polymerization occurs initially which then continues throughout the polymerization. This results in a shorter polymerization cycle, an increased rate of production of PVC and greater production of PVC from PVC reactors.
Although acyl sulfonyl peroxides are quite useful in vinyl chloride polymerizations, they are shock sensitive in the pure form. Hence, they have to be diluted in some manner for safe handling. Acetyl cyclohexylsulfonyl peroxide (ACSP) is currently the only acyl sulfonyl peroxide on the market that is available in commercial quantities. Since ACSP in pure form is a shock sensitive solid (melting point, 33.degree.-35.degree. C), three dilutions of ACSP are commercially available; they are: a) a 28-30% solution of ACSP in dimethyl phthalate (DMP), b) a 20% solution in toluene, and c) a 65% wetted solid. All three formulations have one or more detrimental properties.
The 29% solution of ACSP in DMP has a very narrow recommended storage temperature range of -5.degree. to -9.degree. C. The upper temperature limit was set by thermal stability restrictions whereas the lower temperature limit was set by phase stability restrictions, that is, solids formed at temperatures at or below -9.degree. C. Therefore, the producer as well as the users of this formulation are forced to maintain expensive storage facilities that maintain the temperature between -5.degree. and -9.degree. C. Now recognized is a possible hazard associated with this formulation when stored below -9.degree. C. Unexpected decompositions are possible if this formulation is stored at -15.degree. to -30.degree. C. Apparently, DMP (m.p., 2.degree. C) can crystallize thus increasing the concentration of ACSP in the supernatant liquid at -15.degree. to -30.degree. C. ACSP could then massively and rapidly crystallize from the supernatant liquid thus increasing the temperature of the system to the melting point of ACSP (33.degree. - 35.degree. C) which is above the decomposition temperature of ACSP (18.degree. C). A rapid decomposition is then possible.
The 20% solution of ACSP in toluene contains 80% toluene. This high level of toluene would discourage use of this formulation for producing polyvinyl chloride (PVC) which would be used in food applications. In addition, spillage of this formulation could be hazardous because of the evaporation of low boiling toluene (b.P., 108.degree.-110.degree. C), thus leaving a shock sensitive solid residue. Furthermore, this formulation is significantly less stable than the 28-30% ACSP in DMP and readily develops color during storage.
The 65% wetted solid is not homogenous and is an extremely difficult formulation to handle. Because of the low thermal stability of ACSP, the 65% wetted solid must be stored below 0.degree. C resulting in a solid block because of the water freezing. In this form it must be thawed or hazardously broken-up prior to use. Unlike the liquid formulations the 65% wetted solid cannot be pumped into polymerization reactors.
In order to overcome the detrimental properties of the various ACSP formulations two liquid acyl alkylsulfonyl peroxides, acetyl secheptylsulfonyl peroxide and acetyl 1-methylcyclohexysulfonyl peroxide, were offered for use. However, these peroxides are shock sensitive liquids and have only been offered as safe 50% liquid formulations in solvents such as DMP and isobutyl isobutyrate. These formulations have not been found by the PVC industry as acceptable replacements for the ACSP formulations with their faults.
U.S. Pat. Nos. 3,650,972, 3,466,255 and 3,340,243 disclose prior art acyl sulfonyl peroxide formulations.